Job Scheduling: `cron` and `at`
Automate tasks to run at specific times or intervals using `cron` jobs and `at` commands.
Job Scheduling: `cron` and `at` is a free Linux Command Line Mastery lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Linux Command Line Mastery learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Automating Your Linux Tasks
In Linux, you often need to run tasks automatically. This could be anything from backing up files to generating reports.
Automation saves time and ensures tasks are performed consistently, even when you're not actively at the keyboard.
Introducing `cron` for Recurring Jobs
cron is a powerful utility that helps you schedule commands or scripts to run automatically at specific intervals. Think of it as your personal assistant for repetitive tasks!
These scheduled tasks are often called "cron jobs".
Your Personal `crontab` File
Each user has their own crontab file, which lists their scheduled cron jobs.
- To edit your crontab:
crontab -e - To list your current jobs:
crontab -l - To remove all your jobs:
crontab -r(use with caution!)
When you edit, it typically opens in a text editor like Nano or Vim.
crontab -eUnderstanding `cron` Job Structure
A cron job entry has six parts:
minute hour day_of_month month day_of_week command_to_execute- Minute: 0-59
- Hour: 0-23 (0 is midnight)
- Day of Month: 1-31
- Month: 1-12 (or Jan-Dec)
- Day of Week: 0-7 (0 or 7 is Sunday)
An asterisk (*) means "every" value for that field.
Practical `cron` Examples
Let's look at some common cron job examples you might add to your crontab file.
# Run a script every day at 3:00 AM
0 3 * * * /home/user/daily_backup.sh
# Run a command every Sunday at 10:30 PM
30 22 * * 0 echo "Weekly check!" >> /var/log/weekly.log
# Run every 15 minutes
*/15 * * * * /usr/bin/some_utilityHandy `cron` Shortcuts
For common schedules, cron offers special keywords:
@reboot: Run once after system startup.@hourly: Run once an hour.@daily: Run once a day (midnight).@weekly: Run once a week (midnight Sunday).@monthly: Run once a month (midnight on 1st).@yearly: Run once a year (midnight on Jan 1st).
These keywords replace the first five time fields.
Scheduling Single Tasks with `at`
While cron is for recurring tasks, the at command is perfect for scheduling a command to run only once at a specified future time.
It's useful for tasks that don't need to repeat, like running a report at the end of the day or a specific cleanup task.
How to Use the `at` Command
To schedule a task with at, you provide the time and then type the command(s) you want to run. Press Ctrl+D to finish.
Here's how to schedule a simple message to appear in 1 minute:
echo "echo 'Task completed by at!'" | at now + 1 minuteManaging Your `at` Queue
You can manage your scheduled at jobs:
- To list all pending
atjobs:atq - To remove a specific job:
atrm [job_number]
Each job listed by atq will have a unique job number.
# List all pending 'at' jobs
atq
# Remove the job with ID 42
atrm 42`cron` & `at` Quick Check
Consider the following scenario:
You need to schedule a script named /opt/cleanup.sh to run every Tuesday at 4:45 AM.
Which crontab entry correctly achieves this?
Recap: `cron` and `at`
Great job! You've learned how to automate tasks on Linux:
cronis for scheduling recurring jobs using a `crontab` file and specific time syntax.atis for scheduling commands to run once at a future time.
These tools are essential for system administration and keeping your systems running smoothly without constant manual intervention.
Frequently asked questions
Is the “Job Scheduling: `cron` and `at`” lesson free?
Yes — the full text of “Job Scheduling: `cron` and `at`” is free to read here on the web, and the Linux Command Line Mastery course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Linux Command Line Mastery course, upgrade to CoddyKit PRO.
What will I learn in “Job Scheduling: `cron` and `at`”?
Automate tasks to run at specific times or intervals using `cron` jobs and `at` commands. You practise Linux Command Line Mastery with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Linux Command Line Mastery?
No prior experience is required. Linux Command Line Mastery on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Job Scheduling: `cron` and `at`” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Linux Command Line Mastery lesson?
Yes. Every Linux Command Line Mastery lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.